1. Field of the Invention
The present invention relates to a magnetic sensor, for example, for detecting the speed of revolution of a gear-shaped magnetic rotor.
2. Description of the Related Art
FIG. 7 is a side view of a conventional magnetic sensor, and FIG. 8 is a sectional side view of the magnetic sensor shown in FIG. 7. This magnetic sensor includes a main portion 1 of the sensor and a connector 2 connected to the main portion 1.
The main portion 1 of the sensor includes: a cylindrical case 3 made of a synthetic resin; a main electric circuit 4 placed in the case 3; a rectangular-shaped permanent magnet 5 disposed at an end of the main electric circuit 4; a Hall element 6 serving as a magnetoelectric device disposed in front of the permanent magnet 5; and an O-ring 7 for sealing the connection between the main portion 1 of the sensor and the connector 2.
The main electric circuit 4 includes: a base 8 made of a resin; a plurality of electronic components 9 each encapsulated in its own ceramic package and mounted on the base 8; and interconnecting lines 10 for making electric connections among the electronic components 9.
FIG. 9 is a plan view of an insert 11 from which the interconnecting lines 10 and terminals 17 of the connector 2 will be formed. The insert 11 includes: an interconnecting material 12; a terminal material (not shown); a dual-structure land 14 having a bent portion 13 located at its end; and ties 15.
The main electric circuit 4 may be produced as follows. First, insert molding is performed with the insert 11 so as to form the base 8. The ties 15 are then cut off thereby forming the interconnecting lines 10 from the interconnecting material 12 and also forming the terminals 17 from the terminal material. Then, the respective electronic components 9 are bonded, by means of soldering, to the corresponding lands 14 which serve as their electrodes. Thus, the main electric circuit 4 is obtained. In the above structure, the bent portion 13 of each land 14 is bent in such a manner that the bent portion 13 becomes higher in position than the surface of each interconnecting line 10 and terminal 17 so that molten solder is prevented from flowing outside the land 14 due to interfacial tension.
In the above magnetic sensor, when the gear-shaped magnetic rotor 16, which is made of a magnetic material and disposed near the magnetic sensor, is rotated, the recessed portions 16a and the protruding portions 16b of the magnetic rotor 16 alternately approach and pass by the Hall element 6. This creates a corresponding change in the magnetic field which is applied to the Hall element 6 after emerging from the permanent magnet 5. The above change in the magnetic field is detected as a change in voltage by the Hall element 6. The change in voltage generated by the Hall element 6 is amplified and converted to a pulse signal by the electronic components 9. The resultant electric signal in pulse form is transmitted to a computer unit (not shown) via the terminal 17 so as to detect the speed of revolution of the magnetic rotor 16.
In the conventional magnetic sensor described above, when the main electric circuit 4 is put into the case 3 in the production process, a great force can be accidentally exerted on the end portion of the main electric circuit 4 as shown in FIG. 10(b). Such a force can bend the main electric circuit 4 along its axis A. As a result, a great amount of bending moment occurs at the connector-side end portion of the base 8, and a crack 18 can occur across the base 8 at the connector-side end portion as shown in FIG. 10(a). Those electronic components 9A located on the crack 18 can be damaged (For example, chip breakage), which can result in a fatal failure.
Thus, it is a general object of the present invention to solve the above problem. More specifically, it is an object of the present invention to provide a magnetic sensor whose electric components will never become fatally damaged as the result of an external force.